It seems that botnet usage could have been behind an increase in the number of click fraud clicks cited in the latest Click Fraud Index which monitors such things.

Running for three years now, the index monitors and analyses data from more than 4000 online advertisers and advertising agencies. The Pay Per Click data is collected from online advertising campaigns, large and small, across all leading search engines.

The latest report suggests that while the overall industry average click fraud rate was down 0.1 percent from last quarter to 16.2 percent. it was up from the 15.8 percent rate this time last year. However, the average click fraud rate of PPC advertisements appearing on Google AdSense, Yahoo Publisher Network and other search engine operated schemes was up from 25.6 percent this time last year to 27.6 percent.

Interestingly though, and for the first time, the traffic from botnets was responsible for more than 25 percent of all click fraud traffic.

When it comes to a geographic breakdown, North America rules the roost (although percentage figures were not readily available as I write this) but outside of the US China accounted for 4.3 percent, Russia 3.5 percent and France 3.2 percent.

“Although click fraud rates were relatively unchanged in the second quarter, we found that the methods used to commit click fraud have become increasingly more sophisticated and difficult to detect,” said Tom Cuthbert, president of Click Forensics. “The threat from botnets is the biggest concern as they have grown to cause over one quarter of all click fraud. Online advertisers should be extra vigilant in watching for traffic from botnets in their search marketing campaigns.”